1. Field of the Invention
The present invention relates to an image forming apparatus, and in particular to an image forming apparatus including a recording head and a sensor to detect an ink droplet discharging status of the recording head.
2. Description of the Related Art
As an image forming apparatus such as a printer, a facsimile machine, a copier, a plotter, and a multifunction apparatus combining several of the capabilities of the above devices, for example, an inkjet recording apparatus is known which employs a droplet discharging recording method to discharge ink droplets in image formation.
In such an image forming apparatus, because the recording head discharges ink from nozzles to perform image formation on a sheet of paper, an increase in the viscosity of the ink due to evaporation of the ink solvent from the nozzles, agglomeration of the ink, adhesion of foreign particles, or bubbles may cause defective discharge, thereby degrading image quality.
JP-2007-118264-A discloses an inkjet recording apparatus including a droplet discharge status sensor unit to detect a droplet discharge status from the head, in which when a defective nozzle is detected, recording head maintenance is performed. In the detection of the droplet discharge status, JP-2005-280351-A and JP-2006-110774-A each disclose a method of measuring liquid droplet volume or liquid droplet speed.
As maintenance of the recording head, there are the following methods. Suction method to forcibly suck and discharge a liquid from the nozzle by capping the nozzle surface of the recording head by a cap and driving a suction means connected to the cap; pressurizing method to supply liquid from an ink supply to the recording head under pressure to cause the liquid to be pressed and discharged from the nozzle; and a method combining both of the first two methods. In either case, performing recording head maintenance requires liquid consumption not contributive to image formation.
Accordingly, in maintenance to be performed when any abnormal discharge is detected by the droplet discharge status sensor unit, the liquid is discharged from nozzles capable of properly discharging droplets, resulting in unnecessary consumption of liquid.